This invention relates to a scroll compressor which self-modulates between high and low capacity based upon two distinct criteria.
Scroll compressors are becoming widely utilized in refrigerant compression applications. In a scroll compressor, a first scroll member has a base and a generally spiral wrap extending from the base. A second scroll member is held in a non-orbiting fashion relative to the first scroll member and has a wrap that interfits with a wrap from the first scroll member. The first scroll member is driven to orbit relative to the second, and the interfitting wraps define compression chambers for compressing an entrapped refrigerant.
It is a goal in modern compressor design to be able to provide at least two capacity levels. In some instances, such as when the cooling load on a refrigerant cycle is not particularly high, a lower capacity may be desirable. Less energy is used to compress a lesser amount of refrigerant in low capacity operations. Thus, various modulation schemes have been developed in the prior art.
In one modulation scheme, the compressor moves to low capacity operation when the pressure differential is low. The pressure differential is the delta (difference) of the discharge pressure to the suction pressure. When this quantity is low, there is some indication that lower capacity operation may be in order.
This prior art compressor performs adequately to provide low capacity operation when the compressor is utilized in an air conditioning cycle. However, it is also desirable to use such compressors as part of a heat pump system. In a compressor that is utilized for both air conditioning and heat pump operation, there are times when a relatively low pressure differential is not indicative of a need for low capacity. In particular, if the suction pressure is also low, the compressor may be operating in heat pump mode, and high capacity operation would still be desirable. The prior art will still provide low capacity operation under those circumstances.